The BVOCs Emission Characteristics And Their Contribution To Ozone Generation In Qinling Mountain Region,Shaanxi Province

Volatile organic compounds（VOCs）can produce secondary organic aerosol（SOA）and ozone（O₃）pollution combining with nitrogen oxides（NOx）by photochemical reactions,thus that results increase the urban haze phenomenon and photochemical smog pollution degree.Among all VOCs sources,the Biogenic Volatile Organic Compounds（BVOCs）from natural plant sources play an important role in global air quality issues due to their large emissions and strong reactivity.That researches about the emission characteristics of regional BVOCs emissions and their contribution to ozone generation can provide scientific basis for understanding and preventing ozone pollution.In this dissertation,the mesoscale meteorological model WRFv4.0 is used to simulate the meteorological field,and the MEGANv3.2（Model of Emissions of Gases and Aerosols from Nature）is used to estimate hourly BVOCs emissions at 4×4 km scale in Qinling Mountain region,Shaanxi Province.At the same time,the contribution values of regional BVOCs emissions to ozone generation in surrounding areas were simulated under two scenarios,the combined effect of anthropogenic and biological sources and the individual effect of anthropogenic sources,through combing with the air quality model CMAQv5.3.2.The following main results were achieved:（1）In 2020,the number of BVOCs emitted by vegetation was approximately 29.57×10⁴t,and BVOCs emission per unit area was 4.92 t/km²·a^-1in Qinling Mountain region,Shaanxi Province.Among these,Isoprene and monoterpene accounted for 32.17%and 35.37%of the total BVOCs emissions,respectively,while the other types of BVOCs emissions accounted for 32.46%.（2）The BVOCs emitted by different vegetation types were,trees with 16.69×10⁴t,shrubs with 10.59×10⁴t,crop with 1.64×10⁴t,and grass with 0.65×10⁴t.For the spatial distribution,the general tendency of BVOCs showed higher level in the northwest and southeast region,and a lower level in the northeast and southwest region of Shaanxi Qingling Mountain.For the monthly changes of BVOCs emissions,the number was highest value in August accounting for about 25.78%of the annual emissions.For different season,the BVOCs in summer is highest with 16.00×10⁴t,then autumn 11.16×10⁴t,spring 1.93×10⁴t,winter 0.49×10⁴t.For daily variations,the highest value of BVOCs emissions usually occurs around 14:00 in a day.（3）The monthly emissions of BVOCs in the Shaanxi region of the Qinling Mountains are positively correlated with temperature and photosynthetic active radiation,while negatively correlated with atmospheric pressure.The daily emission rate of BVOCs is positively correlated with temperature and photosynthetic active radiation,while negatively correlated with air pressure and soil moisture.（4）The contribution rate of BVOCs emissions to ozone generation at a monthly average hourly concentration is the highest of 7.096μg/m³in the Shaanxi regions of Qinling Mountain,the highest value is 6.803μg/m³at a monthly maximum 8-hour concentration,and the monthly maximum hourly average concentration is 8.422μg/m³.The contribution ration of isoprene to regional ozone reached 73.79%of the total BVOCs’contribution.Among various cities around the Qinling Mountains,the biggest impact of BVOCs on ozone in the Qinling region is mainly distributed in the northern mountains,with the highest contribution rate to Xi’an,followed by Baoji,Xianyang,and Weinan.